W. K. BROOKS ON THE GENUS SALPA. 223 







5 and 6, a. The history of the egg from this stage to the time when it is 

 fertilized will be understood by the examination of the successive stages 

 shown in the following series of figures, XXII, Figs. 1 and 2 ; XXIII, 

 Figs. 1, 2 and 5 ; XXVI, and XXVII, A, B, and <7; XXV and XXVI, D, 

 E, and F; XXV, O and H; XXXIII, I, J, and K; XXXII, L, M, and N. 



The study of this series shows that, after the stage shown in Plate 

 XXXI, Fig. 5, the only change in these cells is the growth of the yolk 

 and the nucleus, and an increase in the amount of chromatin in the 

 nucleus. Beyond question they must be regarded as eggs at all stages 

 after they have become differentiated from the peripheral cells of the 

 germinal mass ; and while the cells of the embryonic germinal mass are 

 often found in all stages of cell multiplication, my own observations con- 

 firm Seeliger's statement that, after the central cells have become set 

 apart from the others they lose this power, and exhibit no indications of 

 multiplication until they have been fertilized. I do not see how there 

 can be any escape from the admission that the central cells of Fig. 5 and 

 all the later stages are eggs, except by questioning the accuracy of my 

 observations. 



The existence of a cavity between the eggs and the follicle has been 

 affirmed by some writers and denied by others, but it does not seem to 

 be a point of any importance. The inner ends of the follicle cells are 

 sharply defined, and in some specimens I have found them separated, by 

 an empty space, from the yolk, as is shown in the figures in Plate XXXI. 

 In other specimens, however, no such space was found, and the yolk was 

 in close contact with the epithelium on all sides. 



The source of material for the growth of the egg cells is a more 

 important question. The reproductive organ lies in the ventral blood 

 space of the stolon, and as the follicle cells are in direct contact with the 

 nutritive fluid, which is driven through the stolon by the heart of the 

 solitary salpa, they are favorably placed for growth, and in nearly every 

 section their nuclei exhibit indications of multiplication. At the stage 

 shown in Figs. 5 and 6, and occasionally in older stolons, certain bodies 

 of disputed origin are found among the eggs. These bodies are charac- 

 terized by the intensity of their color in stained specimens, and in 

 carmine sections they are usually of a deep and uniform red, but in 

 carefully prepared hasmatoxylin specimens, many of them, the largest 

 ones, are seen to contain a nucleus which is more deeply stained than 

 the surrounding cell body, and this is irregular or amoeboid in shape. 

 Scattered through the yolk are other bodies which agree with the nuclei 



